I've don't have any either (except as 5-channel output that I made to use with an old Rotel amp preamp combo which should be stock pile of many unused things) but have made them in the past (a pain). MSB used to make one as well. I think it was $95 (?) for a one meter cable. Their website is msbtech.com. If you're interested in rolling your own I could send you the pin connections.
Question: that db-25 to eight adapter--would one just leave the other two connectors hanging free? I assume this would work, but I wasn't sure. This makes the Onkyo adapter look very appealing. I also found a great buy on the 8 rca type for only $62 here: .HAVE I didn't find a six rca terminated caqle, though. I would suspect they could fabricate one, however. I tried contacting the same people a couple of times w/ no luck, however. I also found one that looks very nice with Canares here: .cobalt at $107 for 1 meter at $96 and $107 for .5 and 1 meters respectively, rather pricey, but I'm sure very good quality. They're really not bad when one considers the price of six canares from Blue Jeans or Maskeeper would be around $68. I personally really like the db-25 connector because it helps me to keep all of my multi-channel rcas to a minimum.
Andy, the channels are likely labeled (I would hope) so the ones not used would just hang. I originally made one for my old Rotel pre/pro when I changed to more than one amp and I could not use the db25 to db25. I then realized I just needed 5 channels vs. 6 (powered sub from preamp out is the 6th) so I just cut off the one wire. As I noted MSB (and I think Monster too) used to make one. I just looked at the MSB site and it is still listed:
"DB-25 to Six RCA Home Theater Cable for Dolby Digital / DTS outboard processors. Produced with 99.96% pure oxygen free, silver plated copper wire and gold plated terminals. $95"